Explain the PL/SQL function RESULT_CACHE

Add RESULT_CACHE to a function's declaration and Oracle caches (arguments -> result) in a shared area across sessions. A later call with the same arguments returns instantly without running the body. The cache is automatically invalidated when any table the function queries is modified. It fits small, frequently-called, read-mostly lookups (reference data, configuration). Avoid it for functions with session-dependent results, side effects, or that depend on SYSDATE / NLS settings. Monitor with V$RESULT_CACHE_STATISTICS.

CREATE OR REPLACE FUNCTION dept_name(p_id NUMBER)
  RETURN VARCHAR2
  RESULT_CACHE
IS
  v_name departments.department_name%TYPE;
BEGIN
  SELECT department_name INTO v_name
    FROM departments WHERE department_id = p_id;
  RETURN v_name;
EXCEPTION
  WHEN NO_DATA_FOUND THEN RETURN NULL;
END;
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